Seems to me, what ever you added to it, has to be custom work, to fit the lines this has, I sort of remember though, that Ford had a bed that flared out at the top, that could sort of be a beginning to work off of, but whether they made a model of that year, is another matter.
Even though, you would still haft to modify it to make it look right, even if they made one, I believe, you would just haft to find out I guess, I think that year was some where in the 60's or 70's step-side, you would know it if you seen it, cause I think they were the only ones with the flared out at the top on the sides.
Now even if they didn't make such a one, it shouldn't be to hard to duplicate one, it's just a fancy box with the top flared out, with wheel wells in it.
Kerry